Multi-stage piston type compressor

ABSTRACT

In order to achieve a high level of impermeability with a low closing force for the sealing elements of a multistage piston compressor, the overflow channel ( 19 ) in the valve piston ( 9 ) opens into at least two passages ( 26, 27 ) and the sealing plate of the overflow check valve ( 20 ) that is located in the valve piston ( 9 ) is configured as a freely guided closing membrane ( 28 ) with a limited stroke. The passages ( 26, 27 ) of the overflow channel ( 19 ) have different diameters, are arranged on a graduated circle at a radial distance from the axis of the closing membrane ( 28 ) and are completely covered by the closing membrane ( 28 ).

BACKGROUND OF THE INVENTION

The invention relates to a multistage piston compressor comprising avalve casing and a shiftable valve piston formed as a single piece anddriven linearly oscillating by a drive motor, wherein the multistagepiston compressor is furnished with at least one volume changeablelow-pressure chamber with an intake check valve and with at least onevolume changeable high-pressure chamber with a discharge check valve,wherein the valve piston includes a low-pressure piston and ahigh-pressure piston and wherein the low-pressure chamber and thehigh-pressure chamber are connected to each other through an overflowduct, wherein an overflow check valve opening in the direction towardthe high-pressure chamber is inserted in the overflow duct.

Such piston compressors are employed in all technical fields, wherethere exists a need for compressed air. Primarily such pistoncompressors are applied in the vehicle industry for pneumatic suspensionand/or air damping.

Such a piston compressor in a two-stage construction is for exampledescribed in the German printed Patent document DE 197 15 291 A1. Thispiston compressor comprises a compressor casing, where a cylindricallow-pressure chamber with a larger low-pressure piston and a cylindricalhigh-pressure chamber with the smaller high-pressure piston are formedin the compressor casing. Here the low-pressure chamber and thehigh-pressure chamber are disposed on a common axis and the low-pressurepiston and the high-pressure piston are formed to a single piecepressure piston with a common piston rod. The low-pressure chamber isfurnished with an intake with an intake check valve, the high-pressurechamber is furnished with an outlet with a discharge check valve and thetwo pressure chambers are connected by an overflow channel, wherein anoverflow check valve is disposed in the overflow channel. A crank pin ofa crankshaft engages with the common piston rod of the low-pressurepiston and of the high-pressure piston at a right angle alignment,wherein the crankshaft is driven for example by an electric motor andwherein the crankshaft transforms the rotary motion of the crankshaftinto a linear motion at the single piece pressure piston. An oscillatingmotion results at the pressure piston from this linear motion.

The intake check valve, the discharge check valve, and the overflowcheck valve have sealing discs made of spring steel, wherein the sealingdiscs of the spring steel are attached by a middle screw as is the casewith the intake check valve and with the overflow check valve andwherein the sealing discs of spring steel cover in a sealing way severalflow channels disposed on a partial circle, or which sealing discs areheld by a sideways staggered screw as is the case with the dischargecheck valve and which sealing discs seal off a next disposed flowchannel.

These check valves perform their object only in an insufficient way. Itis to be noted that the metallic sealing discs do not seal sufficiently.This can be traced to the fact that the closure and sealing force of thesealing discs is furnished exclusively by the proper tension of thespring steel. Frequently, a tensioning force acts opposite to theclosure and sealing force, wherein the tensioning force starts from theattachment screw and prevents a smooth resting of the sealing disc in apressure balanced state. Leaks occur also by the fact that fatiguesituations occur at the sealing disc in the course of time and that thesealing discs to not rest perfectly at the sealing surface for thisreason. The sealing discs are usually furnished stronger for balancingthese disadvantageous effects. This in turn increases again theincorporation space of such a sealing disc and decreases the volume ofthe corresponding pressure chamber. Such piston compressor's are thennot very powerful. The higher closure force obtained by reinforcing thesealing disc simultaneously increases however the required opening forcefor the free flow through, which opening force has to be furnished bythe system pressure. This also decreases substantially the degree ofeffectiveness of the piston compressor. It has also become apparent thatthe material of the sealing discs fairly quickly fatigues because of thehigh frequencies of the piston compressor and therefore only a smalllifetime of the sealing discs can be recorded.

Finally, the production of the sealing discs out of spring steel is veryinvolved, since on the one hand the material is hard to work with and onthe other hand high requirements are placed on the quality of thesealing face at the sealing disc.

Therefore it is an object of the present Invention to develop a pistoncompressor of the recited kind, wherein the check valves exhibit a lowclosure force and at the same time assure a high sealing effectiveness.

SUMMARY OF THE INVENTION

The object is achieved by a multistage piston compressor of theaforementioned kind with the following properties: The overflow ductjoins at least two passage bore holes; the sealing disc of the overflowcheck valve is formed as a loosely guided and stroke limited sealingmembrane; the passage bore holes of the overflow duct exhibit differentdiameters; the passage bore holes are disposed at an identical radialdistance to the axis of the sealing membrane; and the passage bore holesare completely covered by the sealing membrane.

The new piston compressor eliminates the recited disadvantages of thestate-of-the-art.

The Invention is to be explained in more detail by way of an embodimentexample.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings,

FIG. 1: shows a two-stage piston compressor in the schematic sectionalpresentation,

FIG. 2: shows a detail of the piston compressor with the presentation ofthe intake check valve,

FIG. 3: shows a detail of the piston compressor with the presentation ofthe overflow check valve and of the discharge check valve, and

FIG. 4: shows a top planar view of the valve inserts belonging to theoverflow check valve.

DETAILED DESCRIPTION OF THE DRAWINGS

According to FIG. 1 a two-stage piston compressor comprises in its maincomponents the piston compressor proper 1, a drive motor 2 and anairdrying unit 3.

A valve casing 4 with a cylindrical inner chamber stepped in itsdiameter belongs to the piston compressor 1, wherein the cylindricalinner chamber is subdivided into a low-pressure chamber 5 with a largerdiameter and in a high-pressure chamber 6 with a smaller diameter. Thelow-pressure chamber 5 is sealingly closed to the outside with a valvecasing floor 7 and the high-pressure chamber 6 is sealingly closed tothe outside with a valve casing cover 8. Here the valve casing cover 8is connected to or formed as a single piece with the casing of theairdrying unit 3. A single piece compressor piston 9 is fitted into theinner chamber of the valve casing 4, wherein the compressor piston 9correspondingly comprises a low-pressure piston 10 with a largerdiameter, a high-pressure piston 11 with a smaller diameter, and acommon piston rod 12. A crank case is formed in the outer region of thepiston rod 12, wherein the connecting rod 13 of the crankshaft 14 of thedrive motor 2 engages in right angle alignment in the crank case. Thelow-pressure chamber 5 and the high-pressure chamber 6 have connectionsamong each other and toward the outside.

An intake check valve 15 is thus disposed according to FIG. 2 in thevalve casing floor 7 of the piston compressor 1, wherein the intakecheck valve 15 connects the low-pressure chamber 5 to the atmosphere.Several intake openings 16 disposed on a common circular path and afirst sealing membrane 17 covering all intake openings 16 belong to theintake check valve 15. Here the sealing membrane 17 is fitted into aninternally disposed sunk bore hole, wherein the sunk bore hole exhibitsa ball shaped or an angular bore hole base. A mushroom like attachmentelement 18 placed in the middle fixes the sealing membrane 17 andmaintains the sealing membrane 17 under a light tension on the base ofthe sunk bore hole. Here this tension entered through the attachmentelement 18 is selected such that the first sealing membrane 17 iscapable of rotation in its position and does not protrude and lift offfrom the intake openings 16 in a pressure balanced state. In addition,the sealing membrane 17 and the attachment element 18 are inserted flushinto the sunk bore hole in order not to lose any volume of thelow-pressure chamber 5.

Thus, there is furthermore disposed a passing through overflow channelor duct 19, wherein the overflow duct 19 connects the low-pressurechamber 5 and the high-pressure chamber 6 to each other. And overflowcheck valve 20 is disposed in the high-pressure side joining region ofthis overflow duct 19 according to FIG. 3, wherein the overflow checkvalve 20 functionally connects to each other or separates from eachother the low-pressure chamber 5 and the high-pressure chamber 6. Forthis purpose the joining region of the overflow duct 19 is expanded to achamber 21 having a cross-section of kidney shape, wherein the kidneyshape follows a circular path.

The overflow check valve 20 comprises a pot collar 22 made out ofplastic, wherein the pot collar 22 with its floor rests on the frontface of the high-pressure piston 11 and rests sealingly at the innerwall of the high-pressure chamber 6. The pot collar 22 is broken out inthe region of the overflow duct 19.

A particularly formed valve support 23, which is inserted fittingly intothe inner space of the pot collar 22 and which is shown in more detailin FIG. 4, furthermore belongs to the overflow check valve 20. Thisvalve support 23 consequently has an outer shape which is directed tothe inner chamber of the pot collar 22. A cylindrical recess 24 isinserted from the side of the high-pressure chamber 6, wherein the axisof the cylindrical recess 24 is disposed remote from the axis of thehigh-pressure piston 11 by a certain eccentricity amount. Thiseccentricity amount as well as the size and the radial position of thecylindrical recess 24 assure, that the cylindrical recess 24 is disposedoverlapping with the chamber 25 having kidney shape. The valve support23 is equipped outside of the cylindrical recess 24 with thedistributedly disposed attachment element 25 for a position determininganchoring with the high-pressure piston 11.

A first passage bore hole 26 with a smaller diameter and a secondpassage bore hole 27 with a larger diameter are disposed in the outerradial region of the cylindrical recess 24, wherein the first passagebore hole 26 and the second passage bore hole 27 exhibit an equal ordifferent distance to the axis of the cylindrical recess 24 and whereinthe first passage bore hole 26 and the second passage bore hole 27 areformed such in their position and their extension that they are disposedoverlapping with the chamber 21 having kidney shape of the overflow duct19. Further passage bore holes can be employed in the same kind inaddition to the first passage bore hole 26 and the second passage borehole 27. A freely resting second sealing membrane 28 is fitted with suchplay into the cylindrical recess 24 that the second sealing membrane 28is freely movable in the rotary direction and in axial direction andsuch that the annular intermediate space between the second sealingmembrane 28 and the inner wall of the cylindrical recess 24 are suitablefor air passage. The neighboring edges of the cylindrical recess 24 andof the second sealing membrane 28 are rounded off or, respectively,performed along broken lines.

Furthermore, the cylindrical recess 24 is covered with a stop grid 29,wherein the stop grid 29 delimits on the one hand the axial stroke ofthe second sealing membrane 28 and on the other hand furnishes asubstantially free passage to the released compressed air stream. Herethe structure of the grid stays is freely selected, wherein thebreakouts in the stop grid 29 are provided of such small size that thesecond sealing membrane 28 cannot become clamped. The breakouts can alsobe of different size.

The high-pressure chamber 6 furthermore exhibits a discharge check valve30 or connecting the high-pressure chamber 6 to a user line. Thisdischarge check valve 13 according to FIG. 3 is disposed between thevalve casing 4 and the valve casing cover 8 and comprises a valve plate31 clamped at the circumference and a third sealing membrane 32. Thevalve plate 31 is sealed relative to the valve casing 4 and relative tothe valve casing cover 8 and is furnished with several outlet openings33 disposed on a common part circle. The third sealing membrane 32 isformed as a ring and correspondingly exhibits a middle flow-through borehole 34. The third sealing membrane 32 is held fixedly between the valveplate 31 and the valve casing cover 8, while the flow-through bore hole34 is formed with its diameter sufficiently smaller as the partialcircle diameter of the outlet openings such that the outlet openings 33are fully covered by the third sealing membrane 32.

The third sealing membrane 32 is built in without constructivepretension such that a sealing force results only from the materialspecific own proper tension. The first sealing membrane 17 of the intakecheck valve 15, the second sealing membrane 28 of the overflow checkvalve 20 and the third sealing membrane 32 of the discharge check valve30 are made out of plastic and in particular out of an elastic polymer,which elastic polymer is furnished mainly with a high rupturingstrength, which is elastic polymer is highly stable relative totemperature and which elastic polymer exhibits elastic properties withmemory effect.

The rotary motion of the crankshaft 14 driven by the drive motor 2 istransformed through the connecting rod 13 into an oscillating linearmotion during the operation and the oscillating linear motion istransferred to the compressor piston 9. Therewith the low-pressurepiston 10 and the high-pressure piston 11 move in the same way betweentwo oppositely disposed return points and this way form two low-pressurechamber 5 and high-pressure chamber 6 alternatingly changing in volume.

Such an underpressure is generated here while the low-pressure chamberexpands, where the underpressure lifts the first sealing membrane 17 atits outer circumference and allows outer air to flow in through theintake openings 16. This opening pressure results from the sum of thematerial tension of the sealing membrane 17 and the incorporation causedpretension at the sealing membrane 17. At the same time the underpressure closes the second sealing membrane 28 of the overflow checkvalve 20.

A balanced pressure between the low-pressure chamber 5 and theatmosphere occurs at the first sealing membrane 17 at the upper turningpoint of the motion of the compressor piston 9, whereby the sealingmembrane 17 is pressed by the recited forces of the pretensioning ontothe intake openings 16 and closes the intake openings 16. Lowest passageresistances occur based on the optimum selection of the materialtensions and the incorporation tensions on the one hand duringsuctioning in and on the other hand the first sealing membrane 17 closesin a shortest time after the reaching of the upper turning point. Thisimproves substantially the degree of effectiveness of the pistoncompressor.

The low-pressure chamber 5 is decreased in size with the reverse motionof the compressor piston 9 such that the tensioned air in thelow-pressure chamber 5 is transported under pressure through theoverflow channel 19 to the high-pressure chamber 6. Here the air flowsinitially into the kidney shaped chamber 21 of the overflow duct 19 andcharges from there the second sealing membrane 28 in the region, in theperiphery and in the circumference of the first passage bore hole 26 andof the second passage bore hole 27. A first opening force therewithoperates through the first passage bore hole 26 and a second openingforce operates through the second passage bore hole 27 onto the secondsealing membrane 28, wherein the first opening force and the secondopening force both operate parallel to each other. These two forces areso different, as are the cross sections of the two passage bore holes 26and 27. The freely disposed second sealing membrane 28 is therebybrought into an inclined position and into a rotary motion based on thetangential force components, wherein the radial rotary motion isdirected from the smaller passage bore hole 26 to the larger passagebore hole 27 and wherein the radial rotary motion continuously changesthe position of the second sealing membrane 28 relative to the twopassage bore holes 26, 27. This increases decisively the lifetime of thesecond sealing membrane 28, since the load of the material of thesealing membrane 28 is distributed continuously and therewith apremature overloading of only a certain position of the sealing membrane28 is avoided. Such an overloading leads quickly to rupturing and to afailure of the overflow check valve 20. The freely disposed secondsealing membrane 28 presents only a lowest resistance to the compressedair stream flowing through.

A balanced pressure between the low-pressure chamber 5 and thehigh-pressure chamber 6 prevails again at the lower return point of themotion of the compressor piston 9, wherein the balanced pressure allowsthe overflow check valve 20 to close. The closing occurs extremely quickas a reaction based on the free and low friction guiding of the secondsealing membrane 28.

The compressed air enclosed in the high-pressure chamber 6 is displacedthrough the discharge check valve 30 with the motion of the compressorpiston 9 reducing the high-pressure chamber 6. Here the compressed airpasses the discharge openings 33 released by the third sealing membrane32. The discharge check valve 30 again closes in an extremely quickreaction at the upper return point of the motion of the compressorpiston 9.

LIST OF REFERENCE CHARACTERS

-   -   1 piston compressor    -   2 drive motor    -   3 airdrying unit    -   4 valve casing    -   5 low-pressure chamber    -   6 high-pressure chamber    -   7 valve casing floor    -   8 valve casing cover    -   9 compressor piston    -   10 low-pressure piston    -   11 high-pressure piston    -   12 piston rod    -   13 connecting rod    -   14 crankshaft    -   15 intake check valve    -   16 intake openings    -   17 first sealing membrane    -   18 attachment element    -   19 overflow duct    -   20 overflow check valve    -   21 kidney shaped chamber    -   22 pot collar    -   23 valve support    -   24 cylindrical recess    -   25 attachment element    -   26 first passage bore hole    -   27 second passage bore hole    -   28 second sealing membrane    -   29 stop grid    -   30 discharge check valve    -   31 valve plate    -   32 third sealing membrane.    -   33 outlet opening    -   34 flow-through bore hole

1. A multistage piston compressor comprising a valve casing (4) and ashiftable valve piston (9) formed as a single piece and driven linearlyoscillating by a drive motor (2), wherein the valve piston (9) isfurnished with a low pressure piston (10) and with a high pressurepiston (12), wherein the low pressure piston (10) and the high pressurepiston (11) form at least one volume changeable low-pressure chamber (5)with the intake check valve (15) and with at least one volume changeablehigh-pressure chamber (6) with the discharge check valve (30), andwherein the low-pressure chamber (5) and the high-pressure chamber (6)are connected to each other through an overflow duct (19), wherein anoverflow check valve (20) opening in the direction toward thehigh-pressure chamber (6) is inserted in the overflow duct (19), whereinthe overflow check valve (20) is equipped with a sealing disc, whereinthe overflow duct (19) joins at least two passage bore holes (26, 27),wherein the sealing disc of the overflow check valve (20) is formed as aloosely guided and stroke limited sealing membrane (28), wherein thepassage bore holes (26, 27) of the overflow duct (19) exhibit differentdiameters and wherein the passage bore holes (26, 27) are disposed at anidentical radial distance to the axis of the sealing membrane (28) andwherein the passage bore holes (26, 27) are completely covered by thesealing membrane (28).
 2. The multistage piston compressor according toclaim 1, wherein the sealing membrane (28) is fitted into a recess (24)of a valve support (23) and wherein the sealing membrane (28) is coveredby a stop grid (29).
 3. The multistage piston compressor according toclaim 2, wherein the two passage bore holes (26, 27) go through thevalve support (23) and open into the recess (24) of the valve support(23).
 4. The multistage piston compressor according to claim 1, whereinthe sealing membrane (28) comprises an elastic polymer with memoryproperties.
 5. The multistage piston compressor according to claim 4,wherein the intake check valve (15) is equipped with a first sealingmembrane (17) and wherein the discharge check valve (30) is equippedwith a third sealing membrane (32) and wherein the two sealing membranes(17,32) comprise an elastic polymer with equal properties.
 6. Themultistage piston compressor according to claim 5, wherein the intakecheck valve (15) comprises a valve case floor (7) with an inner faceprovided with a sunk bore hole and is equipped with several intakeopenings (16) disposed on a partial circle, wherein the intake sealingmembrane (17) is fitted into the sunk bore hole and wherein the intakesealing membrane (17) is fixed under tension by a centrally placed andmushroom shaped attachment element (18), wherein the attachment element(18) immerses only to such an extent into the sunk bore hole that theattachment element (18) closes flush with the inner face of the valvecase floor (7) and wherein the first sealing membrane (17) is onlypretensioned by the attachment element (18) to such an extent that thesealing membrane (17) still remains rotatable.
 7. The multistage pistoncompressor according to claim 5, wherein the discharge check valve (30)is furnished with several outlet openings (33) disposed on a common partcircle, wherein the discharge openings (33) are entered into a valveplate (31), wherein the valve plate (31) is tensioned between the valvecasing (4) and a valve casing cover (8) and wherein the third sealingmembrane (32) is formed as a ring and is held with the outercircumference of the third sealing membrane (32) without tension betweenthe valve plate (31) and the valve casing cover (8), wherein the thirdsealing membrane (32) with its inner circumference covers over theoutlet openings (33).